Fig. 155.—Head of the grasshopper.
Fig. 156.—Eyes of a fly.
The eyes of insects are wonderful organs, being both simple and compound. In the grasshopper (Fig. 155) the two are easily seen, the compound eye being the larger. The fly has a remarkable compound eye (Fig. 156), and in the center of the two eyes are three simple ones. The compound eye in the fly is made up of vast numbers of six-sided eyes crowded together, appearing under a glass like a honeycomb; yet each of these facets is a complete eye. In a sectional view of the eye of a beetle (Fig. 157) we can see the nerve that reaches every one. In using the eyes hundreds of images of the same object must reach the brain of the insect, yet the image of but one is seen.
Attached to the head of insects are various sense organs, feelers, or antennæ, which are very ornamental, as in the beetles. The central portion of the skeleton bears the wings. In the beetle the wing covers are formed of hard chitin. When its wings are not in use this insect stores them away in covers provided for the purpose.
Fig. 157.—Sectional view of the eye of a beetle.
The third or last part of the skeleton, the abdomen, often bears a weapon of defense, as a sting or a drill for boring holes in trees, or machines for making silk, as in the spiders. Here also we find a remarkable variety of tails, ranging from that of the dragon fly to the long tail of the scorpion with its dangerous sting or dagger.
The feet of insects would make an interesting chapter alone, ranging from the curious, sucking, padded foot of the fly (Fig. 158) to the claws of others. The anatomy of insects is more or less complicated. The method of breathing is particularly interesting. It is very natural to imagine all animals breathing by the mouth or nostrils, but insects breathe by a singular system of air tubes (Fig 159), or tracheæ, some having lungs as well. The air tubes are wound with threads upon the inside. This preserves their shape and keeps them open. If we examine a grasshopper (Fig. 160), we shall see along the sides openings, which under a powerful microscope resemble eyelike organs (Fig. 161). These are air holes, windows, or spiracles, which lead to the air tubes, and by minute thread-lined tubes reach all over the body. To obtain air, or to breathe, the bee keeps its abdomen continually in motion, forcing air through the body, carrying oxygen to the blood tissues.
